The magnetic disk device such as the hard disk drive has a control system to determine the position of the magnetic head. Unfortunately, the control system often suffers so-called RRO (Repeatable Run Out), which is a cyclic disturbance that occurs in synchronism with the rotation of the magnetic disk. This disturbance is due to the fact that the center of the circular tracks formed on the magnetic disk is offset from the center of revolution of the magnetic disk. Therefore, countermeasures against RRO are taken.
One of such countermeasures is disclosed in Japanese Patent Publication No. 2005-353148 (“Patent Document 1”). This disclosure is concerned with a technology to generate PES (Position Error Signal) for the magnetic head, acquire correction data to suppress RRO components, and record correction data, together with servo data, in the track.
Meanwhile, RRO that affects the control system to determine the position of the magnetic head varies in nature depending on the position on the magnetic disk at which the magnetic head is positioned. This means that some tracks among a plurality of tracks formed on the magnetic disk may not need correction data. Recording correction data in all the tracks reduces the region in which user data is recorded and hence reduces the storage capacity of the magnetic disk. In addition, measuring RRO components for all the tracks and recording correction data increases time required for production.
Incidentally, Patent Document 1 mentioned above suggests the recording of correction data in a portion of tracks, but this method does not prevent the magnetic disk from being reduced in storage capacity because the regions for correction data are secured in all the tracks.